Stand-alone battery powered units--such as utility meters are becoming increasingly prevalent. These utility meters typically have radio frequency (RF) transmitters, or other communications means on-board that transmit usage information to a host computer or other collection means. Typically, these utility meters may also require means for communicating information, independent of the RF transmitter. This independent communications means may be used for diagnostic purposes via a service tool communications interface.
Contemporary service tool communications interfaces between a stand-alone battery powered utility meter and a host computer are typically electrically connected via a mechanical connection means--such as a detachable connector. This is costly because it requires a mechanical connection means robust enough to withstand many couplings. Also, if the utility meter is mounted outdoors--which they typically are, the mechanical connection needs to withstand fairly adverse weathering and still operate reliably. As a practical matter, mechanical connections have a relatively short fatigue life.
Other service tool communications interfaces are optical in nature. These not only provide electrical isolation but can be more reliable because there is no mechanical interface to wear out as in the case of the electrically connected interface.
One problem with this type of interface is that ambient light can interfere with operation of the optical interface. For instance, solar energy might appear to be a signal that the utility meter might consider valid communications information. The problem of ambient light interference can be prevented by physically shrouding the optical reception mechanism, but this approach has all of the disadvantages of the mechanical interface such as cost and wear-out.
Another problem with an optical interface is that it can require that the utility meter has to be powered on continually in anticipation of communication reception. Continuously powering the utility meter is very undesirable because the meter's battery will be required to provide energy to run the utility meter full time. This would require a relatively large battery which is costly and bulky.
Another approach would be to operate the utility meter in a low power mode (low battery energy drain) with limited functionality. For instance, in this low power consumption mode the utility meter could periodically attempt communications with the host unit by looking for a host-transmitted signal via on-board optical components. Then, when a recognizable host-transmitted signal is received, the utility meter could be fully powered and have full functionality available. This approach requires separating the utility meter's internal circuitry into a low current consumption section that is continuously powered, and a higher current consumption section that is powered only when the low current consumption section signals that a valid host-transmitted signal has been received via the optical interface. While the utility meter is fully powered it can perform its full function which may include reception of service tool information via the optical interface and RF transmission of usage information. Then, once the service tool communications sequence is completed, the utility meter's higher current consumption section can be powered-down or put to sleep to conserve on-board battery power.
One problem with this approach is that the optical reception circuitry that needs to receive and recognize the host-transmitted signal needs to have sufficient complexity to recognize a host-transmitted signal pattern--rather than just the presence of a perceived host-transmitted signal, to prevent ambient light from invoking the utility meter's higher current consumption section. This relatively more complex circuitry requires relatively higher power consumption and adds to the bulk of the utility meter. Furthermore, because of the additionally-required complexity, the field reliability of the utility meter is reduced.
What is needed is an improved optical service tool communications interface for communicating between a stand-alone battery powered unit--such as a utility meter and a host computer that is simple, compact, reliable, insensitive to ambient light and operates with a low current consumption.